Endocrine System, Hormones
& Feedback Mechanisms
How the endocrine system controls everything
The Endocrine System
I.
II.
III.
IV.
General Overview
Basic Anatomy
Control of the endocrine system
Specific endocrine events
I. A General Overview
• ES (endocrine system) and homeostasis
• Anatomy
– Endocrine glands, cells, neurosecretory cells
– Hormones
– Target cells
• ES as a Control System
– Hormone + target = change in cell function
(return to homeostasis)
ES and Homeostasis
• Homeostasis
Feedback Mechanisms
• Stimulus
– change in homeostatic environment
– signal sent to CNS
• Response
– signal sent from CNS
– produce effect
– body returns to homeostasis
Basic ES cont.
• ES and NS = 2 main
control systems of
body
• Endocrine organs
located throughout
body
• Actions mediate all
tissues
• Control of ES through
feedback mechanisms
II. ES anatomy basics
A. Exocrine gland –NOT ES! =(
– Ducts
– Lumen and surfaces
B. Endocrine gland - Hormones
A.
Hypothalamus, Pituitary, Pineal Gland,
Thyroid, parathyroid, thymus, adrenal,
pancreas, testes, ovaries
– Chemical messengers
– Blood stream
Hormones
• Chemical messenger
– Secreted by endocrine
gland
– Specific to target
– Activate cellular
change
– Of 4 different chemical
types
4 Classes of Hormones
1.
2.
3.
4.
Peptide/ Protein
Steroid
Amine
Eicosanoid
Protein/Peptide Hormones
•
•
•
•
Hydrophilic
Large
Can't fit through membrane
Most hormones
– Example: Insulin
Peptide Hormones cont.
• Short 1/2-life
• Pancreas
– Insulin/glucagon
• Hypothalamus
– RH (releasing
hormones)
– RIH (release inhibiting
hormones)
Steroid Hormones
•
•
•
•
•
Small
Hydrophobic/Lipophilic
Travel in blood with carrier
Cytoplasmic receptors
change protein synthesis
– Example: estradiol
Steroid hormones cont.
• Genomic effect
– Activates genes
– Directs synthesis of
new proteins
• Lag time between
hormone binding and
effect = long time.
• Gonads & placenta
• Adrenal cortex
Amine
• Synthesized from a single
amino acid
• Melatonin from tryptophan
• Thyroid hormone from
tyrosine
• Catecholamines
• Released from adrenal
medulla / adrenal
gland
• Epinephrine,
Norepinephrine,
Dopamine
Eicosanoid
• Produced from 20-carbon fatty
acid
• Produced in all cells except
RBCs
• Inflammation
• (Omega 3, Omega 6)
• Essential Fatty Acids
Hormone + Receptor
Where are Hormones Made ?
The H-P-A
Hypothalamic-Pituitary Axis
• Most feedback loops run through this axis
• HPA mediates growth, metabolism, stress
response, reproduction.
• is secondarily in charge of almost
everything else.
D. Neurosecretory Cells
1. Specialized neurosecretory
cells
–
Synthesize and secrete hormones
2. Extend from
HYPOTHALAMUS to
POSTERIOR PITUITARY
2. Neurosecretory cells in
Hypothalamus
• Nuclei synthesize and secrete
hormones
• Antidiuretic Hormone
(ADH)
– Responsible for increasing
water absorption in the
collecting ducts of the kidney
nephron
• Oxytocin
– Social Behavior
• Sexual behavior – Pair bonding?
Why is the Hypothalamus so
Important?
• Secretes regulatory
homones
• RH = Pituitary releasing
hormones
• RIH = Pituitary release
inhibiting hormones
• "Directs" pituitary
– Ex. A releasing
hormone controls the
release of other
hormones.
STIMULUS
Hypothalamus
Releasing Hormone
(Release-Inhibiting Hormone)
Pituitary
Stimulating Hormone
Gland
Hormone
Target
Hypothalamic Hormomes
• Release Inhibiting Hormones
– Somatostatin
• growth hormone-inhibiting hormone
– Prolactin release inhibiting hormone-PIH
• Peptide hormone involved in lactation
• Releasing Hormones
– Thyrotropin releasing hormone-TRH
– Growth hormone releasing hormone-GHRH
E. Pituitary gland
MASTER GLAND
• Anterior and
posterior portions
1. Posterior connected
to hypothalamus by
infundibulum
2. Anterior connected
via blood stream
Control of Endocrine Function
A. Positive
B. or Negative
Feedback
mechanisms
•
Self-regulating
system
STIMULUS
Hypothalamus
Releasing Hormone
(Release-Inhibiting
Hormone)
Pituitary
Stimulating Hormone
Gland
Hormone
Target
A. Positive Feedback
• Not common
• Classic example:
Action of
OXYTOCIN on
uterine muscle during
birth.
Positive Feedback
•
•
•
•
Baby pushes on cervix
Nervous signal to Hypothalamus
Hypothal. manufactures OXY
OXY transported to POSTERIOR
PITUITARY & released
• OXY stimulates uterine contraction
• Loop stops when baby leaves birth canal
B. Negative Feedback
• Most common control
mechanism
• Level of hormone in
blood or body’s return
to homeostasis shuts
off loop at
hypothalamus and
pituitary
Basic Structure of Feedback
Loop
•
•
•
•
•
•
Environmental Stimulus
Stimulates Control Center (Brain-hypothal.)
Hypothalamic hormones stim. Pituitary
Pituitary hormone stim. Target area
Target area produces change
Change acts negatively or positively on the cycle.
IV. Specific Endocrine Events
A.
B.
C.
D.
Thyroid Hormone
Growth Hormone
Adrenal Cortex Hormones
Sex Steroids
A. Thyroid Hormone
• “Thyronines” act on nearly every
cell in the body. Made from “I”
–
–
–
–
Metabolic rate
Protein synthesis
Bone growth
Sensitivity to Cetacholamines
(Adrenaline)
– Vitamin absorption
Growth
B. Growth Hormone
•
•
•
•
•
Stimulus = Tissue growth/ repair
Hypothalamus releases GHRH
Anterior Pituitary releases GH
Protein synthesis, growth, etc.
GH and release of somatostatin shuts off
GHRH and GH release
GH as Juvenile
GH = pituitary dwarfism
Adrenal Gland
• Adrenal gland located atop kidney
• Outer part = cortex
– Secretes Cortisol (stress), Androgens (used in
males, precursor of estrogen), Aldosterone
(electrolyte absorption)
• Inner part = medulla
– SNS control
– Secretes EPI & NEPI (fight or flight)
Adrenal Insufficiency
• Addison’s disease--hyposecretion of
cortisol
• Weight loss, hypoglycemia
• Inability to handle stress
4. Sex Steroids
•
•
•
•
•
Stimulus = low circulating T or E
Hypothalamus = GnRH (Gonadotropin)
Anterior Pituitary = FSH(Folicle stimulating)
Gonads produce T and E
High T and E shut off GnRH and FSH
Importance
• Reproduction/Mating Behavior
• Formation of reproductive organs
– gonads
– brain
4 Classes of Hormones
A.
B.
C.
D.
Peptide/ Protein
Steroid
Amine
Eicosanoid
2M
1M
2M
2M